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Subject[PATCH] /dev/mem: Avoid overwriting "err" in read_mem()
Successes in probe_kernel_read() would mask failures in copy_to_user()
during read_mem().

Reported-by: Brad Spengler <spender@grsecurity.net>
Fixes: 22ec1a2aea73 ("/dev/mem: Add bounce buffer for copy-out")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/char/mem.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 052011bcf100..ffeb60d3434c 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -137,7 +137,7 @@ static ssize_t read_mem(struct file *file, char __user *buf,

while (count > 0) {
unsigned long remaining;
- int allowed;
+ int allowed, probe;

sz = size_inside_page(p, count);

@@ -160,9 +160,9 @@ static ssize_t read_mem(struct file *file, char __user *buf,
if (!ptr)
goto failed;

- err = probe_kernel_read(bounce, ptr, sz);
+ probe = probe_kernel_read(bounce, ptr, sz);
unxlate_dev_mem_ptr(p, ptr);
- if (err)
+ if (probe)
goto failed;

remaining = copy_to_user(buf, bounce, sz);
--
2.7.4

--
Kees Cook
Pixel Security

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